Alfalfa is an important animal forage crop in many areas of the world. The methods of biotechnology have been applied to alfalfa for improvement of the agronomic traits and the quality of the product. One such agronomic trait important in alfalfa production is herbicide tolerance, in particular, tolerance to glyphosate herbicide.
Alfalfa is a perennial leguminous plant (Medicago sativa) of the family Leguminosae (pulse family), the most important pasture and hay plant in North America, also grown extensively in Argentina, S Europe, and Asia. Alfalfa has high yield, high protein content, and prolific growth. However, unlike most grain or fiber crops from which weeds are separated at harvest, weeds are often harvested along with the forage crop, potentially reducing quality. Reductions in quality are often in the form of lower protein content and feed digestibility. Weeds in new alfalfa stands especially reduce yield and crop quality. The major weeds in new alfalfa fields are annuals, such as green foxtail, pigweed, and lambsquarters. Winter annuals, such as flixweed, blue mustard, shepherdspurse, other mustards and downy brome, are more likely to cause serious weed problems in established stands. Perennial weeds, such as foxtail barley and dandelion, are also common weed problems in established alfalfa. Bindweed and Canada thistle are weeds in alfalfa for which there are currently no good control methods. A herbicide tolerant alfalfa event would be a useful trait for managing weeds and maintaining the quality of the forage.
N-phosphonomethylglycine, also known as glyphosate, is a well-known herbicide that has activity on a broad spectrum of plant species. Glyphosate is the active ingredient of Roundup® (Monsanto Co.), a safe herbicide having a desirably short half-life in the environment. When applied to a plant surface, glyphosate moves systemically through the plant. Glyphosate is phytotoxic due to its inhibition of the shikimic acid pathway, which provides a precursor for the synthesis of aromatic amino acids. Glyphosate inhibits the enzyme 5-enolpyruvyl-3-phosphoshikimate synthase (EPSPS) found in plants. Glyphosate tolerance can also be achieved by the expression of EPSPS variants that have lower affinity for glyphosate and therefore retain their catalytic activity in the presence of glyphosate (U.S. Pat. Nos. 5,633,435; 5,094,945; 4,535,060, and 6040,497). Enzymes that degrade glyphosate in plant tissues (U.S. Pat. No. 5,463,175) are also capable of conferring cellular tolerance to glyphosate. Such genes are used for the production of transgenic crops that are tolerant to glyphosate, thereby allowing glyphosate to be used for effective weed control with minimal concern of crop damage. For example, glyphosate tolerance has been genetically engineered into corn (U.S. Pat. No. 5,554,798), wheat (Zhou et al. Plant Cell Rep. 15:159-163, 1995), soybean (WO 9200377) and canola (WO 9204449). The transgenes for glyphosate tolerance and the transgenes for tolerance to other herbicides, e.g. bar gene, (Toki et al. Plant Physiol., 100:1503-1507, 1992; Thompson et al. EMBO J. 6:2519-2523, 1987; phosphinothricin acetyltransferase DeBlock et al. EMBO J., 6:2513-2522, 1987, glufosinate herbicide) are also useful as selectable markers or storable markers and can provide a useful phenotype for selection of plants linked with other agronomically useful traits.
The expression of foreign genes in plants is known to be influenced by their chromosomal position, perhaps due to chromatin structure (e.g., heterochromatin) or the proximity of transcriptional regulation elements (e.g., enhancers) close to the integration site (Weising et al., Ann. Rev. Genet 22:421-477, 1988). For this reason, it is often necessary to screen a large number of events in order to identify an event characterized by optimal expression of an introduced gene of interest. For example, it has been observed in plants and in other organisms that there may be a wide variation in levels of expression of an introduced gene among events. There may also be differences in spatial or temporal patterns of expression, for example, differences in the relative expression of a transgene in various plant tissues, that may not correspond to the patterns expected from transcriptional regulatory elements present in the introduced gene construct. For this reason, it is common to produce hundreds to thousands of different events and screen those events for a single event that has desired transgene expression levels and patterns for commercial purposes. An event that has desired levels or patterns of transgene expression is useful for introgressing the transgene into other genetic backgrounds by sexual outcrossing using conventional breeding methods. Progeny of such crosses maintain the transgene expression characteristics of the original transformant. This strategy is used to ensure reliable gene expression in a number of varieties that are well adapted to local growing conditions.
It would be advantageous to be able to detect the presence of a particular event in order to determine whether progeny of a sexual cross contain a transgene of interest. In addition, a method for detecting a particular event would be helpful for complying with regulations requiring the premarket approval and labeling of foods derived from recombinant, crop plants, for example. It is possible to detect the presence of a transgene by any well known polynucleic acid detection method such as the polymerase chain reaction (PCR) or DNA hybridization using polynucleic acid probes. These detection methods generally focus on frequently used genetic elements, such as promoters, terminators, marker genes, etc. As a result, such methods may not be useful for discriminating between different events, particularly those produced using the same DNA construct unless the sequence of chromosomal DNA (“flanking DNA”) adjacent to the inserted transgene DNA is known. An event-specific PCR assay is discussed, for example, by Windels et al. (Med. Fac. Landbouww, Univ. Gent 64/5b:459-462, 1999), who identified glyphosate tolerant soybean event 40-3-2 by PCR using a primer set spanning the junction between the insert transgene and flanking DNA, specifically one primer that included sequence from the insert and a second primer that included sequence from flanking DNA. Transgenic plant event specific DNA detection methods have also been described in US 20020013960 and WO 0227004.
This invention relates to the glyphosate herbicide tolerant alfalfa events J-101 and J-163, and to the DNA molecules contained in these alfalfa plants that are useful in detection methods for glyphosate tolerant alfalfa and progeny thereof.